package com.lq.dubbo.rocketmq.shop.util;

/**
 * @program: dubborocketmqshop
 * @description: id生成器(采用Twitter公司, 利用雪花算法)进行id生成
 * id没有使用自增,如果数据量大进行分库的时候,自增可能导致id重复
 * @author: LQ
 * @create: 2021-06-03 14:08
 */
public class IdWorker {
    private final static long START_STMP = 1480166465631L;
    // 序列号占用的位数
    private final static long SEQUENCE_BIT = 12;
    // 机器标识占用的位数
    private final static long MACHINE_BIT = 5;
    // 数据中心占用的位数
    private final static long DATACENTER_BIT = 5;

    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
    /**
     * 数据中心
     */
    private long datacenterId;
    /**
     * 机器标识
     */
    private long machineId;

    /**
     * 序列号
     */
    private long sequence = 0L;
    /**
     * 上一次时间戳
     */
    private long lastStmp = -1L;

    public IdWorker(long datacenterId, long machineId) throws IllegalAccessException {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalAccessException("datacenterId can't be greater than MAX_DATACENTER_NUM or less then 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalAccessException("machineId can't be greater than MAX_MACHINE_NUM or less then 0");

        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    public synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("clock moved backwards. Refusing to generate id");
        }
        if (currStmp == lastStmp) {
            // 相同毫秒内,序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            // 同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            // 不同毫秒内,序列号置为0
            sequence = 0L;
        }
        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT // 数据中心部分
                | machineId << MACHINE_LEFT //机器标识部分
                | sequence; // 序列号部分
    }

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }
    private long getNewstmp(){
        return System.currentTimeMillis();
    }

    public static void main(String[] args) throws IllegalAccessException {
        IdWorker idWorker = new IdWorker(2,3 );
        for (int i = 0 ;i<10;i++){
            System.out.println(idWorker.nextId());
        }
    }
}
